The present invention relates to a circuit board on which an electronic component is mounted, a method for manufacturing the circuit board, and a display device and electronic equipment employing the circuit board.
A technology for directly mounting electronic components, such as IC chips, on a FPC (Flexible Printed Circuit) board is currently in use to keep pace with a current trend to a smaller, thinner, and lighter board, to meet a bendable design requirement, and to accomplish high yield using a roll-to-roll process. Since such a technology does not need inner leads, unlike the TAB (Tape Automated Bonding) technology, thin copper foils work, and the promotion of fine pitch design in wiring is easy.
FIG. 10 is a cross-sectional view showing a conventional structure in which an electronic component is mounted on an FPC board. As shown, an input electrode 450a of an IC chip 450 and an input wiring 420a beforehand formed on the base film 410 are electrically connected to each other through electrically conductive particles 460a dispersed within an adhesive agent 460. Similarly, an output electrode 450b of the IC chip 450 and an output wiring 420b beforehand formed on the base film 410 are electrically connected to each other through electrically conductive particles 460a dispersed within an adhesive agent 460.
Since the base film 410, as a base material for the FPC board, typically contains organic film, such as PI (polyimide), which is pervious to moisture, moisture penetrates from the side (the IC chip mounting surface of the FPC)(the underside in FIG. 10) opposite a mounting side into the base film 410 and reaches a wiring formation plane (active surface of IC chip 450) of the IC chip 450. For this reason, the reliability of the IC chip is compromised, or light leakage of light transmitted through the base film 410 degrades the reliability of the IC chip. This disadvantage becomes more pronounced if the base film 410 is made thinner.
The present invention has been developed in view of the above problems, and it is an object of the present invention to provide a circuit board, including an electronic component and an wiring board, that prevents a drop in the reliability and performance of the electronic component, such as a mounted IC chip, a method for manufacturing the circuit board, and a display device and electronic equipment employing the circuit board.
(1) A circuit board of the present invention includes a wiring board including a base material having insulation and flexibility, and a wiring layer arranged on the base material, and an electronic component electrically connected to the wiring layer and mounted on the wiring board, and a covering section for covering the base material on the side opposite the mounting side of the electronic component, in an area which, at least, partly overlaps a mounting area of the electronic component in a plan view, wherein the covering section is electrically isolated from the wiring layer and the electronic component and has moisture resistance.
In accordance with the present invention, moisture penetrating through the base material from the side opposite the mounting side of the electronic component is fully blocked by the covering section. This arrangement reduces the possibility that moisture penetration degrades the reliability and performance of the electronic component and the wiring layer in the area of the wiring board where the electronic component is mounted. When the electronic component, typically a semiconductor device such as an IC chip, is mounted on the wiring board, the circuit board is subject to short circuits and half-short/half-open circuits under the effect of moisture, because the pitches of a wiring pattern of the wiring board in the mounting area are typically fine. The circuit board of the present invention reduces the creation of such a problem.
(2) In a circuit board of the present invention, the covering section is a dummy wiring layer.
In accordance with the present invention, the covering section is constructed using the same facility that is used to construct the wiring layer.
(3) In a circuit board of the present invention, the covering section is a resin layer.
(4) In a circuit board of the present invention, the covering section has a light shielding property.
In accordance with the present invention, the covering section completely shields light penetrating through the base material from the side opposite the mounting area of the electronic component. This arrangement reduces a drop in the performance of the electronic component mounted on the wiring layer due to a light leakage.
(5) A circuit board of the present invention further includes a resin encapsulation section for encapsulating, by resin, the area where the electronic component and the wiring layer are electrically connected to each other.
In accordance with the present invention, the resin encapsulation section encapsulates, by resin, the area where the electronic component and the wiring layer are electrically connected to each other. This arrangement reduces the possibility that the reliability of the area where the electronic component and the wiring layer are electrically connected to each other is degraded under the influence of moisture.
(6) A circuit board of the present invention, according to one of (1) through (4), further includes an anisotropic conductive film, interposed between the electronic component and the wiring layer, for electrically connecting the electronic component to the wiring layer.
If the electronic component is bonded to the wiring board using the anisotropic conductive film in this way, a bonding step and a molding step in the TAB (Tape Automated Bonding) mounting are carried out in a single step, and the manufacturing process is advantageously shortened.
(7) In a circuit board of the present invention, the base material and the wiring layer are bonded together with no intervening adhesive layer interposed therebetween.
When the wiring layer is directly connected to the base material without any intervening adhesive layer in this way, the circuit board is free from a current leakage due to the adhesive agent and a swelling of the adhesive agent, and the flexibility of the wiring board is increased.
(8) In a circuit board of the present invention, according to one of (1) through (7), the base material includes a plurality of layers, and the covering section is arranged between the plurality of the layers.
The circuit board is a multi-layered board in which a base material is made up of a plurality of layers, and the covering section is arranged between layers of the base material. With the covering section arranged between the plurality of the layers, the area of the covering section is easily set to be equal to or larger than the bonding area of the electronic component. When the area of the covering section is set to be equal to or larger than the bonding area of the electronic component, the possibility of the penetration of moisture and light from outside the covering section is further reduced.
(9) A display device of the present invention includes one of the above-described circuit boards, and a flat panel including a connection terminal to which the circuit board is electrically connected.
(10) In a display device of the present invention, the flat panel is a liquid-crystal panel including a pair of opposing substrates, and a liquid crystal encapsulated between the pair of substrates, and the connection terminal is formed at least on one of the pair of substrates.
(11) In a display device of the present invention, the electronic component mounted on the circuit board includes a drive semiconductor device.
(12) Electronic equipment of the present invention includes a display device according to (11), and a video signal processing circuit for processing a video signal input to the display device.
(13) A method of the present invention for manufacturing a circuit board according to one of (1) through (7) includes an electronic component mounting step for mounting the electronic component onto the front side of the wiring board through pressure bonding, and a covering section forming step for forming the covering section on the back side of the wiring board, subsequent to the electronic component mounting step.
In accordance with the present invention, the covering section is formed on the back side of the wiring board after the electronic component is mounted onto the front side of the wiring board through pressure bonding, and the covering section thus reinforces the base material of the wiring board that might have been damaged in the course of the mounting of the electronic component through pressure bonding. This arrangement reduces the possibility of the penetration of moisture from the back side of the wiring board, and thus reduces the possibility that moisture penetrating from the back side of the wiring board is transmitted through the base material and causes any problems in the mounting area of the electronic component. These problems may include a short circuit or a half-short/half-open circuit, for example.
(14) A method of the present invention for manufacturing a circuit board according to one of (1) through (7), includes a covering section forming step for forming the covering section on the back side of the wiring board, and an electronic component mounting step for mounting the electronic component onto the front side of the wiring board through pressure bonding, subsequent to the covering section forming step.
In accordance with the present invention, the electronic component is mounted onto the front side of the wiring board through pressure bonding, after the covering section is formed on the back side of the wiring board. Since the wiring board is reinforced by the covering section formed on the back side of the wiring board, there is less possibility that the base material of the wiring board is damaged in the course of the mounting of the electronic component through pressure bonding. This arrangement reduces the possibility of the penetration of moisture from the back side of the wiring board, and thus reduces the possibility that moisture penetrating from the back side of the wiring board is transmitted through the base material and causes any problems in the mounting area of the electronic component. These problems may include a short circuit or a half-short/half-open circuit, for example.